CPR feedback method and apparatus

ABSTRACT

The present invention comprises a cardiopulmonary resuscitation (CPR) feedback device and a method for performing CPR. A chest compression detector device is provided that measures chest compression during the administration of CPR. The chest compression detector device comprises a signal transmitter operably positioned on the chest of the patient and adapted to broadcast a signal, and a signal receiver adapted to receive the signal. The chest compression detector device also comprises a processor, operably connected to the signal transmitter and the signal receiver. The processor repeatedly analyzes the signal received to determine from the signal a series of measurements of compression of the chest, and feedback is provided to the rescuer based on the series of measurements.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/209,701, filed Aug. 15, 2011, now U.S. Pat. No. 8,600,522, issuedDec. 3, 2013, which is a divisional of U.S. patent application Ser. No.11/420,515 filed May 26, 2006, now U.S. Pat. No. 8,010,190, issued Aug.30, 2011, which are hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to devices and techniques useful forassisting in the administration of cardiopulmonary resuscitation (CPR).More particularly, the present invention relates to a device and methodfor using ultrasonic signals to determine the depth of chest compressionduring CPR.

BACKGROUND OF THE INVENTION

CPR is a technique used by a rescuer in an emergency situation to getoxygen into a victims blood when that persons heart has stopped beatingand/or they are not breathing spontaneously. When performing CPR therescuer creates blood circulation in the victims body by periodicallycompressing the victims chest.

The American Heart Association (AHA) recommends that the rescuer pressdown on the sternum with a force sufficient to depress it between 1.5and 2.0 inches. The current recommended rate for these periodicdepressions is 100 times a minute, and 30 chest compressions should begiven for every two rescue breaths. Chest compressions produce bloodcirculation as the result of a generalized increase in intrathoracicpressure and/or direct compression of the heart. The guidelines state“blood circulated to the lungs by chest compressions will likely receiveenough oxygen to maintain life when the compressions are accompanied byproperly performed rescue breathing.” A victim can be kept alive usingCPR provided the rescuer(s) are able to continue delivering properlyperformed chest compressions and rescue breaths.

Administering CPR is a challenging and physically demanding procedurewhich is performed under stressful life and death circumstances.Performing chest compressions and rescue breaths is a also a physicallydemanding task, and can be difficult to properly coordinate. The qualityof chest compressions and rescue breaths delivered to a patient candegrade for a number of reasons, including fatigue, lack of visualreferences, and rescue situation stresses. As rescuers become fatigued,they may not realize that they are compressing a patient's chest withinadequate force. The more fatigued a rescuer becomes, the less he maybe compressing a patient's chest, and the more likely the effectivenessof the CPR is reduced.

To be most effective, the rescuer must attempt to keep the chestcompressions uniform both in terms of the time between successive chestcompressions and the amount of force used for each compression. Keepinguniform intervals for chest compressions is difficult the longer the CPRmust be administered as the stresses associated with a rescue situationcan cause the rescuer's sense of time to be distorted. Keeping the chestcompressions uniform in terms of force is difficult not only because offatigue, but also because it is difficult for the rescuer to estimatethe force being applied based on the distance which the chest is beingcompressed. Much of the difficulty in estimating the distance which thechest is being compressed stems from the relative position of therescuer and the victim. When performing chest compressions, the rescuerpositions his or her shoulders directly above the victim's chest, andpushes straight down on the sternum. In this position, the rescuer'sline of sight is straight down at the victim's chest. With this line ofsight, the rescuer has no visual reference point to use as a basis forestimating the distance that he or she is compressing the chest.

The aforementioned problems may be compounded by a number of factors,such as when the length of time that CPR is being administeredincreases, and when the rescuer is not accustomed to rescue situations(for example when CPR is being performed by a lay person or a relativelyinexperienced rescuer).

A number of devices have been proposed to assist a rescuer in applyingCPR, as described, for example, in U.S. Pat. No. 6,125,299 to Groenke etal. Most of these devices measure either the force applied to apatient's chest, or measure the acceleration of the patient's chest (orrescuer's hand), or both. The measured force may be compared to a knowndesired value, and a prompt may be issued from the device instructing arescuer to compress the patient's chest harder or softer. Displacementof a patient's chest can be calculated by double integrating a measuredacceleration, and a prompt may be issued from the device instructing arescuer to compress the patient's chest harder or softer. Many prior artdevices also measure the frequency of chest compressions given, and areable to prompt a rescuer to increase or decrease the rate ofcompressions being administered.

Although measuring acceleration is an acceptable method of determiningchest compression during CPR, the method is not without its flaws. Forexample, signal error, external acceleration error, and drift error inthe compression starting points can all create inaccuracies in chestcompression measurement. External acceleration error can arise from useof the accelerometer in a moving vehicle such as an ambulance, or fromunusual patient attitudes, such as partially sitting up.

For these reasons, there is a need in the art for a practical devicethat more accurately measures the compression of a patient's chestduring CPR, and provides feedback to a rescuer in the event that thedisplacement and frequency of chest compressions falls outside a presetcriteria. A device of this type will provide rescuers with coachingwhich will enable them to deliver chest compressions consistently andbeneficently.

SUMMARY OF THE INVENTION

The present invention, through various embodiments, provides acardiopulmonary resuscitation (CPR) feedback device and a method forperforming CPR. In one embodiment, a chest compression detector deviceis provided that measures chest compression during administration ofCPR. The chest compression detector device comprises a signaltransmitter operably positioned on the chest of the patient and adaptedto broadcast a signal, and a signal receiver adapted to receive thesignal. The chest compression detector device also comprises aprocessor, operably connected to the signal transmitter and the signalreceiver. The processor repeatedly analyzes the signal received todetermine from the signal a series of measurements of compression of thechest, and feedback is provided to the rescuer based on the series ofmeasurements.

The CPR feedback device according to another embodiment is used inconjunction with an automatic external defibrillator (AED). The deviceincludes a chest compression sensor on the chest of a patient, adaptedto broadcast a signal toward the spine of a patient and adapted toreceive a reflection of the signal. The chest compression sensor is inelectrical communication with a control system of the AED, the controlsystem processing a signal communicated from the chest compressionsensor related to the magnitude of the chest compressions and to thefrequency of chest compressions. The AED also includes a prompting meansoperably coupled to the AED control system for receiving communicationsignals from the AED control system and for communicating prompts to therescuer for use by the rescuer in resuscitating the victim. The promptsare related to the signal communicated to the AED control system by thechest compression sensor.

The present invention also comprises a method of performingcardiopulmonary resuscitation on a patient. The method includes thesteps of providing a compression detection device proximate the sternumof the patient such that the device moves in unison with the chest ofthe patient during compression of the chest, broadcasting a signal fromthe compression detection device, receiving the signal at thecompression detection device, compressing the chest of a patient, usinga processor operably in communication with the compression detectiondevice to determine from the signal a series of measurements ofcompression of the chest relative to the spine of the patient as thestep of compressing the chest of the patient is performed, andautomatically providing feedback to a rescuer performing the step ofcompressing the chest of the patient as part of cardiopulmonaryresuscitation in response to the series of measurements that advises therescuer whether the step of compressing the chest is being performedwithin a predetermined set of guidelines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a chest compression detection deviceaccording to one embodiment of the present invention.

FIG. 2 is a perspective view of a measurement device applied to apatient being used with an automatic external defibrillator according toone embodiment of the present invention.

FIG. 3 is a perspective view of a measurement device being used on apatient.

FIG. 4 is a side view of the measurement device applied to a patient.

FIG. 5 is a perspective view of a rescue kit according to one embodimentof the present invention.

FIG. 6 is a perspective view of a measurement device applied to apatient being used with an automatic external defibrillator according toone embodiment of the present invention.

FIG. 7 is a perspective view of a measurement device applied to apatient being used with an automatic external defibrillator according toone embodiment of the present invention.

FIG. 8 is a block diagram of an automatic external defibrillator.

FIG. 9 is a perspective view of a sensor for use with an embodiment ofthe present invention.

FIG. 10 is a perspective view of an automatic external defibrillatorincorporating a measurement device within a pair of electrodes accordingto one embodiment of the present invention.

FIG. 11 is a side view of the measuring device applied to a patientaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-known methods,procedures, and components have not been described in detail so as tonot unnecessarily obscure aspects of the present invention.

Referring to FIGS. 1-5, a chest compression detection device 10 isdepicted. Device 10 includes a signal transmitter 14, a signal receiver16, and a processor 18. In one embodiment, device 10 comprises anultrasonic transducer. Transmitter 14 and receiver 16 are integratedinto device 10. Processor 18 is operably coupled to both transmitter 14and receiver 16. Processor 18 instructs transmitter 14 to send out anultrasonic pulse 20, then counts the elapsed time for pulse 20 to reachreceiver 16. Processor 18 can then calculate the distance of an objectfrom device 10. Device 10 further includes an audio speaker 26, a powersource 28, and may include a communicator 30. Power source 28 provideselectrical power to all components in device 10.

Device 10 is placed on a victim's chest 22, in the location where chestcompressions are to be administered. In one embodiment, device 10 ispreferably located on the victim's sternum, generally between thevictim's nipples, and in line with a victim's spine 24. A rescuer placeshis hands over device 10 and begins to administer chest compressions.Processor 18 instructs transmitter 14 to emit ultrasonic pulses 20.Pulses 20 are directed towards victim's spine 24, reflected, andreceived by receiver 16. Processor 18 counts the time it takes for pulse20 to travel from transmitter 14 to receiver 16. Knowing the velocity atwhich sound waves travel, processor 18 can then calculate the distancethat pulse 20 traveled. By collecting data of the distance traveled bymany successive pulses, processor 18 can determine the amount that achest 22 is being compressed by a rescuer. In one embodiment, the numberof pulses 20 emitted per second is sufficient to give processor 18sufficient data to accurately calculate chest compression depth. Onceprocessor 18 has calculated chest compression depth, processor 18compares that depth to a desired range of compression depth.

In order for CPR to be effective, chest compressions are preferablybetween one and one half (1.5) inches and two (2) inches. In the eventthat processor 18 determines chest 22 is not being compressed enough,processor 18 is adapted to provide feedback to the rescuer preferablythrough speaker 26. Similarly, if processor 18 determines that chest 22is being over-compressed, processor 18 uses speaker 26 to providefeedback to the rescuer. Such feedback may be in the form of a voiceprompt stating “push harder” in the event of under-compression of chest22, or “push softer” in the event of over-compression of chest 22. Suchfeedback may also be some other audible prompt, such as beeps, or mayinclude visual instructions, tactile feedback, or any combinationthereof.

Processor 18 is also adapted to monitor the rate at which compressionsare given and provide feedback to a rescuer if the rate of chestcompressions falls outside of a predetermined range of rates. If therate of chest compressions being delivered by the rescuer is less thanthe desired range, processor 18 causes speaker 26 to provide feedback tothe rescuer, such as with a voice prompt stating “push faster,” or otherfeedback prompt. If the rate of chest compressions being delivered bythe rescuer is greater than the desired range, processor 18 causesspeaker 26 to provide feedback to the rescuer, such as with a voiceprompt stating “push slower,” or other feedback prompt. It should beapparent that audio speaker 26 may be supplemented with, or replaced by,various indicators such as lights, a visual display, vibratingmechanism, and so on.

In another embodiment of the present invention depicted in FIG. 2,device 10 does not include a speaker, rather device 10 includes acommunicator 30. Communicator 30 is adapted to communicate chestcompression data to automatic external defibrillator (AED) 12, usingwireless means such as acoustic signals, optical signals, Bluetooth, IR,or RF. AED 12 includes an audio speaker 32 and/or a visual display 34.Audio speaker 32 and visual display 34 are each adapted to providefeedback to a rescuer in response to the chest compression data receivedfrom communicator 30 of device 10.

In such an embodiment, device 10 may comprise part of a rescue kit 36,depicted in FIG. 5. Rescue kit 36 may include basic first aid items suchas a face shield, rubber gloves, scissors, and so on, in addition to achest compression detection device. Because AED units are relativelyexpensive, it may be cost prohibitive to equip a large building or areawith a sufficient number of AEDs to ensure the close proximity of an AEDto a cardiac arrest victim. However, a large building or area may beoutfitted with many lower cost rescue kits 36. In the case of a rescueattempt on a victim, a first rescuer can quickly obtain a rescue kit 36and begin CPR with device 10 while a second rescuer can retrieve an AED12 from a central location in the building or area. As AED 12 gets intocommunication range with device 10, device 10 and AED 12 begincommunicating via communicator 30. AED 12 can then immediately beginproviding prompts to a first rescuer using audio speaker 32 and/orvisual display 34. Once first electrode 38 and second electrode 40 ofAED 12 are attached to a victim, AED 12 may also prompt a rescuer usingaudio speaker 32 and/or visual display 34 to momentarily cease chestcompressions while a defibrillation shock is administered.

In another embodiment of the present invention depicted in FIG. 6, achest compression detection device 110 is provided as part of an AED112. Device 110 is removably coupled to AED 112 with wires 140. AED 112includes a first electrode 115, a second electrode 117, and a processor118 as depicted in FIG. 8. Device 110 includes a transmitter 114 and areceiver 116, whereby device 110 is adapted to emit ultrasonic pulse 20from transmitter 114 into a patient's chest 122 and receive pulse 20 atreceiver 116 subsequent to pulse 20 being reflected off a patient'sspine 24, as shown in FIG. 4. The time elapsed between the transmittingand the receiving of a pulse 20 is used by processor 118 to calculatethe distance traveled by pulse 20. By collecting data of the distancetraveled by many successive pulses, processor 118 can determine thedistance that a chest 122 is being compressed. In one embodiment, thenumber of pulses 20 emitted per second is sufficient to give processor18 sufficient data to accurately calculate chest compression depth.

Once processor 118 has calculated chest compression depth, processor 118compares that depth to a desired range of compression depth (ideallybetween one and one half (1.5) inches and two (2) inches.) If processor118 determines that chest 122 is not being compressed enough, processor118 causes AED 112 to provide feedback to a rescuer performing chestcompressions. The prompt may be a voice prompt stating “push harder,” orother feedback prompt using an audio speaker 126, or may be a visualprompt using visual display 128, or both. If processor 118 determinesthat chest 122 is being compressed too much, feedback may be provided tothe rescuer with a voice prompt stating “push softer” using speaker 126,or a visual prompt using visual display 128, or both.

Processor 118 is also adapted to monitor the rate at which chestcompressions are given, and provide feedback to a rescuer if the rate ofchest compressions falls outside of a predetermined range of rates. Ifthe rate of chest compressions being delivered by the rescuer is lessthan the desired range, processor 118 causes AED 112 to provide feedbackto the rescuer to increase the rate of compressions. Such feedback maybe a voice prompt stating “push faster,” or other audible prompt fromspeaker 126, a visual prompt provided by visual display 128, or otherfeedback. If the rate of chest compressions being delivered by therescuer is greater than the desired range, processor 118 causes AED 112to provide feedback to the rescuer to decrease the rate of compressions.Such feedback may be a voice prompt stating “push slower,” or otheraudible prompt from speaker 126, a visual display provided by visualdisplay 128, or other feedback. In an alternative embodiment depicted inFIG. 7, device 110 lacks wires 140, but includes a wireless means fortransmitting data to AED 112, such as, for example, a wirelesscommunicator 130, wherein said wireless means may employ acousticsignals, optical signals, BLUETOOTH® wireless technology standard thatuses short-wavelength ultra high frequency waves, IR, or RF.

In one embodiment, AED 112 includes an electrical system such as thatdisclosed in U.S. Pat. No. 6,125,299 to Groenke et al., which is herebyincorporated by reference. FIG. 8 is a block diagram of electricalsystem 70 of AED 112. A digital microprocessor-based control system 72is used for controlling overall operation of AED 112 and for deliveringa defibrillation shock pulse through electrodes 115 and 117 viaconnector 67 and lead wires. The electrical control system 72 furtherincludes an impedance measuring circuit for testing the interconnectionand operability of electrodes 115 and 117 to detect several faults.Control system 72 includes a processor 118 interfaced to program memory76, data memory 77, event memory 78 and real time clock 79. Theoperating program executed by processor 118 is stored in program memory76. Electrical power is provided by the battery 80 which is removablypositioned within the battery compartment of AED 112 and is connected topower generation circuit 84.

Power generation circuit 84 is also connected to lid switch 90, watchdog timer 92, real time clock 79, and processor 118. Lid switch 90 suchas, for example, a Hall-effect or magnetic read relay switch, providessignals to processor 118 indicating whether the lid of AED 112 is openor closed. Data communication port 64 is coupled to processor 118 fortwo-way serial data transfer using an RS-232 protocol. Rescue switch 63,maintenance indicator 61, the indicator lights of diagnostic displaypanel 62, the voice circuit 94, and piezoelectric audible alarm 96 arealso connected to processor 118. Voice circuit 94 is connected tospeaker 126. In response to voice prompt control signals from processor118, circuit 94, and speaker 126 generate audible voice prompts forconsideration by a rescuer.

High voltage generation circuit 86 is also connected to and controlledby processor 118. Circuits such as high voltage generation circuit 86are generally known, and disclosed, for example, in the commonlyassigned Persson et al. U.S. Pat. No. 5,405,361, which is herebyincorporated by reference. In response to charge control signalsprovided by processor 118, high voltage generation circuit 86 isoperated in a charge mode during which one set of semiconductor switches(not separately shown) cause a plurality of capacitors (also not shown),to be charged in parallel to the 12V potential supplied by powergeneration circuit 84. Once charged, and in response to dischargecontrol signals provided by processor 118, high voltage generationcircuit 86 is operated in a discharge mode during which the capacitorsare discharged in series by another set of semiconductor switches (notseparately shown) to produce the high voltage defibrillation pulses. Thedefibrillation pulses are applied to the patient by electrodes 115 and117 through connector 67 connected to the high voltage generationcircuit 86.

Impedance measuring circuit 66 is connected to both connector 67 andreal time clock 79. Impedance measuring circuit 66 is interfaced toprocessor 118 through analog-to-digital (A/D) converter 69. Impedancemeasuring circuit 66 receives a clock signal having a predeterminedmagnitude from clock 79, and applies the signal to electrodes 115 and117 through connector 67. The magnitude of the clock signal receivedback from electrodes 115 and 117 through connector 67 is monitored byimpedance measuring circuit 66. An impedance signal representative ofthe impedance present across electrodes 115 and 117 is then generated bycircuit 66 as a function of the ratio of the magnitudes of the appliedand received clock signals (i.e., the attenuation of the appliedsignal).

For example, if electrodes 115 and 117 within an unopened electrodepackage are connected by the lead wires and connector 68 is properlyconnected to connector 67 on AED 112, a relatively low resistance (e.g.,less than about 10 ohms) is present across electrodes 115 and 117. Ifthe hydrogel adhesive on electrodes 115 and 117 is too dry, or theelectrodes 115 and 117 are not properly positioned on the patient, arelatively high resistance (e.g., greater than about two hundred fiftyohms) will be present across the electrodes 115 and 117. The resistanceacross electrodes 115 and 117 will then be between about twenty-five andtwo hundred fifty ohms when fresh electrodes 115 and 117 are properlypositioned on the patient with good electrical contacts. It should benoted that these resistance values are given as exemplary ranges and arenot meant to be absolute ranges. The impedance signal representative ofthe impedance measured by circuit 66 is digitized by A/D converter 69and provided to processor 118.

Impedance measuring circuit 65 is connected to connector 67 and realtime clock 79, and is interfaced to processor 118 throughanalog-to-digital (A/D) converter 69. Impedance measuring circuit 65receives a clock signal having a predetermined magnitude from clock 79,and applies the signal to chest compression detection device 110 throughconnector 67. The magnitude of the clock signal received back fromdevice 110 through connector 32 is monitored by impedance measuringcircuit 65. An impedance signal representative of the impedance presentacross device 110 is then generated by impedance measuring circuit 65 asa function of the ratio of the magnitudes of the applied and receivedclock signals (i.e., the attenuation of the applied signal). Theimpedance signal representative of the impedance measured by circuit 65is digitized by A/D converter 69 and provided to processor 118.

Referring now to FIG. 9, the present invention may also incorporate apulse oximetry sensor 142. Sensor 142 is operably coupled to AED 112,and is placed on a victim's fingertip, earlobe, or other relatively thinpart of a victim's body. Sensor 142 utilizes selected wavelengths oflight to noninvasively determine the saturation of oxyhemoglobin (SpO₂)in a victim's blood. Based on SpO₂ levels, an estimate of the oxygencontent of a victim's blood can be determined. Sensor 142 is utilizedwhile chest compressions are administered by a rescuer. Processor 118receives information from sensor 142, and compares oxygen level readingsto a desired range of oxygen levels. Low oxygenation may be due to notcompressing the chest of a victim far enough, or at a fast enough rate.In the event that oxygen levels from sensor 142 are too low, processor118 causes AED 112 to provide feedback to the rescuer to increase thedepth of, or rate of compressions. Such feedback may be a voice promptfrom speaker 126 stating “push harder” or “push faster,” a visual promptprovided by visual display 128, or other feedback. Conversely, highoxygenation may be due to compressing the chest of a victim too far, orat too fast of a rate. In the event that oxygen levels from sensor 142are too high, processor 118 causes AED 112 to provide feedback todecrease the depth of, or rate of compressions. Such feedback may be avoice prompt from speaker 126 stating “push softer” or “push slower,” avisual prompt provided by visual display 128, or other feedback.

Referring now to FIG. 10, a further embodiment of the present inventionis shown. Rescuers may be reluctant to conduct chest compressions whileputting their hands on an electric device, out of fear of electrocution.Although accidental electrocution is highly improbable, the embodimentdepicted in FIG. 10 does not require a rescuer to conduct chestcompressions while pushing on an electronic chest compression detectiondevice. Rather, first electrode 115 is adapted to include a signaltransmitter 114, and second electrode 117 is adapted to include a signalreceiver 116. First electrode 115 and second electrode 117 are operablycoupled to processor 118 in AED 112. Pulse 20 (not shown) is emittedfrom transmitter 114 in first electrode 115, triangulated off of spine124, and received by receiver 116 in second electrode 117. Electrodes115 and 117 may be placed on a victim's chest 122 as shown in FIG. 10.

Alternatively, one electrode may be placed on a victim's chest 122generally over the heart, while the other electrode is placed on avictim's back, such that the two electrodes and the heart are inline, asshown in FIG. 11. In such an arrangement, transmitter 114 in electrode115 directs a pulse 20 towards receiver 116 in electrode 117, and pulse20 is not reflected before being received. Further, those skilled in theart will readily recognize that electrodes 115 and 117 and/or chestcompression detection device 110 may be placed in locations on a patientother than those explicitly shown in the figures or described hereinwithout deviating from the spirit or scope of this invention.

In order to enhance the reflectivity of pulse 20, a reflector pad may beused in conjunction with all embodiments of the present invention. Thereflector pad may be placed generally proximate the victim's back and isadapted to increase the reflectivity of pulse 20, and thereby increasethe ability of receiver 116 to receive the reflected pulse 20.

The present invention may be embodied in other specific forms withoutdeparting from the essential attributes thereof; therefore, theillustrated embodiments should be considered in all respects asillustrative and not restrictive, reference being made to the appendedclaims rather than to the foregoing description to indicate the scope ofthe invention.

The invention claimed is:
 1. A method of performing cardiopulmonaryresuscitation on a patient comprising the steps of: providing acompression detection device proximate the sternum of the patient suchthat the device moves in unison with the chest of the patient duringcompression of the chest; broadcasting an ultrasonic pulse signal fromthe compression detection device; receiving the ultrasonic pulse signalat the compression detection device; compressing the chest of a patientwith the compression detection device; using a processor operably incommunication with the compression detection device to determine fromthe ultrasonic pulse signal a series of measurements of compressiondistance of the chest relative to the spine of the patient as the stepof compressing the chest of the patient is performed; and automaticallyproviding feedback to a rescuer performing the step of compressing thechest of the patient as part of cardiopulmonary resuscitation inresponse to the series of measurements that advises the rescuer whetherthe step of compressing the chest is being performed within apredetermined set of guidelines.
 2. The method of claim 1, wherein thestep of broadcasting an ultrasonic pulse signal from the compressiondetection device further comprises broadcasting an ultrasonic pulsesignal from the compression detection device into the chest towards thespine of the patient.
 3. The method of claim 2, wherein the step ofreceiving the ultrasonic pulse signal at the compression device furthercomprises receiving the ultrasonic pulse signal at the compressiondevice following reflection of at least a portion of the ultrasonicpulse signal off of the spine of the patient.
 4. The method of claim 3further comprising: using the processor to determine a timing associatedwith compression of the chest based on the series of measurements ofcompression of the chest; and automatically providing feedback to therescuer performing the step of compressing the chest of the patient aspart of cardiopulmonary resuscitation in response to the series oftiming that advises the rescuer whether the step of compressing thechest is being performed within a predetermined set of guidelines for arecommended timing of chest compressions for cardiopulmonaryresuscitation.
 5. The method of claim 4, wherein the guidelines areselected from the group consisting of chest displacement, compressionrate, and blood oxygen levels.